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 $248.32   6.743%   $265.0642   $265.06   $265.05   $265.10  
  Purchase #2 $194.84   3.434%   $201.5308   $201.53   $201.55   $201.50  
  Purchase #3 $153.66   4.400%   $160.421   $160.42   $160.40   $160.40  
  Purchase #4 $54.52   10.267%   $60.1176   $60.12   $60.10   $60.10  
  Purchase #5 $235.50   3.678%   $244.1617   $244.16   $244.15   $244.20  
  Purchase #6 $10.43   4.467%   $10.8959   $10.90   $10.90   $10.90  
  Purchase #7 $193.75   9.740%   $212.6213   $212.62   $212.60   $212.60  
  7 purchase totals = $1,091.02       $1,154.8125   $1,154.81   $1,154.75   $1,154.80