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 $32.72   3.164%   $33.7553   $33.76   $33.75   $33.80  
  Purchase #2 $149.94   4.801%   $157.1386   $157.14   $157.15   $157.10  
  Purchase #3 $216.72   4.353%   $226.1538   $226.15   $226.15   $226.20  
  Purchase #4 $91.75   8.427%   $99.4818   $99.48   $99.50   $99.50  
  Purchase #5 $209.93   4.718%   $219.8345   $219.83   $219.85   $219.80  
  Purchase #6 $85.97   10.756%   $95.2169   $95.22   $95.20   $95.20  
  Purchase #7 $163.59   10.316%   $180.4659   $180.47   $180.45   $180.50  
  7 purchase totals = $950.62       $1,012.0468   $1,012.05   $1,012.05   $1,012.10