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 $51.68   12.267%   $58.0196   $58.02   $58.00   $58.00  
  Purchase #2 $228.72   12.654%   $257.6622   $257.66   $257.65   $257.70  
  Purchase #3 $74.96   13.317%   $84.9424   $84.94   $84.95   $84.90  
  Purchase #4 $179.39   6.415%   $190.8979   $190.90   $190.90   $190.90  
  Purchase #5 $235.94   11.519%   $263.1179   $263.12   $263.10   $263.10  
  Purchase #6 $179.38   10.527%   $198.2633   $198.26   $198.25   $198.30  
  Purchase #7 $162.36   12.572%   $182.7719   $182.77   $182.75   $182.80  
  7 purchase totals = $1,112.43       $1,235.6752   $1,235.67   $1,235.60   $1,235.70