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 $201.72   5.459%   $212.7319   $212.73   $212.75   $212.70  
  Purchase #2 $202.88   11.723%   $226.6636   $226.66   $226.65   $226.70  
  Purchase #3 $18.69   10.177%   $20.5921   $20.59   $20.60   $20.60  
  Purchase #4 $113.52   3.252%   $117.2117   $117.21   $117.20   $117.20  
  Purchase #5 $81.33   8.625%   $88.3447   $88.34   $88.35   $88.30  
  Purchase #6 $201.32   4.654%   $210.6894   $210.69   $210.70   $210.70  
  Purchase #7 $180.44   9.594%   $197.7514   $197.75   $197.75   $197.80  
  7 purchase totals = $999.90       $1,073.9848   $1,073.97   $1,074.00   $1,074.00