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 $245.85   8.404%   $266.5112   $266.51   $266.50   $266.50  
  Purchase #2 $129.77   13.283%   $147.0073   $147.01   $147.00   $147.00  
  Purchase #3 $60.41   7.663%   $65.0392   $65.04   $65.05   $65.00  
  Purchase #4 $244.52   11.220%   $271.9551   $271.96   $271.95   $272.00  
  Purchase #5 $215.31   9.342%   $235.4243   $235.42   $235.40   $235.40  
  Purchase #6 $197.40   4.384%   $206.054   $206.05   $206.05   $206.10  
  Purchase #7 $43.78   4.130%   $45.5881   $45.59   $45.60   $45.60  
  7 purchase totals = $1,137.04       $1,237.5792   $1,237.58   $1,237.55   $1,237.60