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 $59.96   8.642%   $65.1417   $65.14   $65.15   $65.10  
  Purchase #2 $240.84   4.814%   $252.434   $252.43   $252.45   $252.40  
  Purchase #3 $237.64   13.624%   $270.0161   $270.02   $270.00   $270.00  
  Purchase #4 $91.68   3.139%   $94.5578   $94.56   $94.55   $94.60  
  Purchase #5 $48.75   4.547%   $50.9667   $50.97   $50.95   $51.00  
  Purchase #6 $152.52   8.501%   $165.4857   $165.49   $165.50   $165.50  
  Purchase #7 $47.73   3.488%   $49.3948   $49.39   $49.40   $49.40  
  7 purchase totals = $879.12       $947.9968   $948.00   $948.00   $948.00