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 $67.84   11.354%   $75.5426   $75.54   $75.55   $75.50  
  Purchase #2 $141.48   13.553%   $160.6548   $160.65   $160.65   $160.70  
  Purchase #3 $134.25   3.412%   $138.8306   $138.83   $138.85   $138.80  
  Purchase #4 $194.88   3.449%   $201.6014   $201.60   $201.60   $201.60  
  Purchase #5 $113.98   7.766%   $122.8317   $122.83   $122.85   $122.80  
  Purchase #6 $224.72   9.725%   $246.574   $246.57   $246.55   $246.60  
  Purchase #7 $49.52   11.742%   $55.3346   $55.33   $55.35   $55.30  
  7 purchase totals = $926.67       $1,001.3697   $1,001.35   $1,001.40   $1,001.30