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 $58.40   8.338%   $63.2694   $63.27   $63.25   $63.30  
  Purchase #2 $109.90   11.251%   $122.2648   $122.26   $122.25   $122.30  
  Purchase #3 $57.89   13.692%   $65.8163   $65.82   $65.80   $65.80  
  Purchase #4 $147.79   9.713%   $162.1448   $162.14   $162.15   $162.10  
  Purchase #5 $101.77   8.471%   $110.3909   $110.39   $110.40   $110.40  
  Purchase #6 $101.67   11.708%   $113.5735   $113.57   $113.55   $113.60  
  Purchase #7 $150.27   7.270%   $161.1946   $161.19   $161.20   $161.20  
  7 purchase totals = $727.69       $798.6543   $798.64   $798.60   $798.70