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 $54.72   13.615%   $62.1701   $62.17   $62.15   $62.20  
  Purchase #2 $160.37   10.838%   $177.7509   $177.75   $177.75   $177.80  
  Purchase #3 $143.86   4.774%   $150.7279   $150.73   $150.75   $150.70  
  Purchase #4 $243.59   13.240%   $275.8413   $275.84   $275.85   $275.80  
  Purchase #5 $202.33   4.693%   $211.8253   $211.83   $211.85   $211.80  
  Purchase #6 $29.91   13.448%   $33.9323   $33.93   $33.95   $33.90  
  Purchase #7 $186.42   11.148%   $207.2021   $207.20   $207.20   $207.20  
  7 purchase totals = $1,021.20       $1,119.4499   $1,119.45   $1,119.50   $1,119.40