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 $238.92   13.477%   $271.1192   $271.12   $271.10   $271.10  
  Purchase #2 $150.96   12.773%   $170.2421   $170.24   $170.25   $170.20  
  Purchase #3 $87.94   7.588%   $94.6129   $94.61   $94.60   $94.60  
  Purchase #4 $38.51   8.466%   $41.7703   $41.77   $41.75   $41.80  
  Purchase #5 $63.37   9.770%   $69.5612   $69.56   $69.55   $69.60  
  Purchase #6 $147.93   12.769%   $166.8192   $166.82   $166.80   $166.80  
  Purchase #7 $222.27   10.791%   $246.2552   $246.26   $246.25   $246.30  
  7 purchase totals = $949.90       $1,060.3801   $1,060.38   $1,060.30   $1,060.40