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 $74.71   13.526%   $84.8153   $84.82   $84.80   $84.80  
  Purchase #2 $164.61   6.343%   $175.0512   $175.05   $175.05   $175.10  
  Purchase #3 $173.64   11.116%   $192.9418   $192.94   $192.95   $192.90  
  Purchase #4 $80.90   7.656%   $87.0937   $87.09   $87.10   $87.10  
  Purchase #5 $91.83   9.503%   $100.5566   $100.56   $100.55   $100.60  
  Purchase #6 $48.32   13.474%   $54.8306   $54.83   $54.85   $54.80  
  Purchase #7 $135.97   7.295%   $145.889   $145.89   $145.90   $145.90  
  7 purchase totals = $769.98       $841.1782   $841.18   $841.20   $841.20