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 $197.65   7.104%   $211.6911   $211.69   $211.70   $211.70  
  Purchase #2 $58.75   11.431%   $65.4657   $65.47   $65.45   $65.50  
  Purchase #3 $71.58   5.457%   $75.4861   $75.49   $75.50   $75.50  
  Purchase #4 $110.25   7.346%   $118.349   $118.35   $118.35   $118.30  
  Purchase #5 $161.80   3.405%   $167.3093   $167.31   $167.30   $167.30  
  Purchase #6 $241.25   5.700%   $255.0013   $255.00   $255.00   $255.00  
  Purchase #7 $73.65   5.874%   $77.9762   $77.98   $78.00   $78.00  
  7 purchase totals = $914.93       $971.2787   $971.29   $971.30   $971.30