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 $174.86   13.108%   $197.7806   $197.78   $197.80   $197.80  
  Purchase #2 $243.56   8.185%   $263.4954   $263.50   $263.50   $263.50  
  Purchase #3 $132.40   4.546%   $138.4189   $138.42   $138.40   $138.40  
  Purchase #4 $250.85   8.460%   $272.0719   $272.07   $272.05   $272.10  
  Purchase #5 $195.26   8.809%   $212.4605   $212.46   $212.45   $212.50  
  Purchase #6 $110.90   11.284%   $123.414   $123.41   $123.40   $123.40  
  Purchase #7 $48.31   5.270%   $50.8559   $50.86   $50.85   $50.90  
  7 purchase totals = $1,156.14       $1,258.4972   $1,258.50   $1,258.45   $1,258.60