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 $89.65   4.381%   $93.5776   $93.58   $93.60   $93.60  
  Purchase #2 $48.56   12.456%   $54.6086   $54.61   $54.60   $54.60  
  Purchase #3 $97.85   12.211%   $109.7985   $109.80   $109.80   $109.80  
  Purchase #4 $206.56   8.415%   $223.942   $223.94   $223.95   $223.90  
  Purchase #5 $87.96   12.561%   $99.0087   $99.01   $99.00   $99.00  
  Purchase #6 $111.61   8.863%   $121.502   $121.50   $121.50   $121.50  
  Purchase #7 $30.98   5.749%   $32.761   $32.76   $32.75   $32.80  
  7 purchase totals = $673.17       $735.1984   $735.20   $735.20   $735.20