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 $177.56   13.483%   $201.5004   $201.50   $201.50   $201.50  
  Purchase #2 $210.71   4.840%   $220.9084   $220.91   $220.90   $220.90  
  Purchase #3 $71.70   9.513%   $78.5208   $78.52   $78.50   $78.50  
  Purchase #4 $193.85   7.277%   $207.9565   $207.96   $207.95   $208.00  
  Purchase #5 $202.71   3.506%   $209.817   $209.82   $209.80   $209.80  
  Purchase #6 $70.50   7.237%   $75.6021   $75.60   $75.60   $75.60  
  Purchase #7 $41.96   5.540%   $44.2846   $44.28   $44.30   $44.30  
  7 purchase totals = $968.99       $1,038.5898   $1,038.59   $1,038.55   $1,038.60