Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $242.95   11.588%   $271.103   $271.10   $271.10   $271.10  
  Purchase #2 $137.57   7.462%   $147.8355   $147.84   $147.85   $147.80  
  Purchase #3 $243.78   12.790%   $274.9595   $274.96   $274.95   $275.00  
  Purchase #4 $180.47   12.475%   $202.9836   $202.98   $203.00   $203.00  
  Purchase #5 $101.91   13.687%   $115.8584   $115.86   $115.85   $115.90  
  Purchase #6 $249.51   9.392%   $272.944   $272.94   $272.95   $272.90  
  Purchase #7 $166.28   6.157%   $176.5179   $176.52   $176.50   $176.50  
  7 purchase totals = $1,322.47       $1,462.2019   $1,462.20   $1,462.20   $1,462.20