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 $45.61   4.182%   $47.5174   $47.52   $47.50   $47.50  
  Purchase #2 $195.89   3.609%   $202.9597   $202.96   $202.95   $203.00  
  Purchase #3 $250.80   5.849%   $265.4693   $265.47   $265.45   $265.50  
  Purchase #4 $48.56   4.372%   $50.683   $50.68   $50.70   $50.70  
  Purchase #5 $209.80   13.368%   $237.8461   $237.85   $237.85   $237.80  
  Purchase #6 $48.29   6.338%   $51.3506   $51.35   $51.35   $51.40  
  Purchase #7 $199.45   5.668%   $210.7548   $210.75   $210.75   $210.80  
  7 purchase totals = $998.40       $1,066.5809   $1,066.58   $1,066.55   $1,066.70