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 $31.87   6.224%   $33.8536   $33.85   $33.85   $33.90  
  Purchase #2 $160.52   10.329%   $177.1001   $177.10   $177.10   $177.10  
  Purchase #3 $163.48   9.574%   $179.1316   $179.13   $179.15   $179.10  
  Purchase #4 $230.39   4.634%   $241.0663   $241.07   $241.05   $241.10  
  Purchase #5 $43.59   5.841%   $46.1361   $46.14   $46.15   $46.10  
  Purchase #6 $62.54   3.550%   $64.7602   $64.76   $64.75   $64.80  
  Purchase #7 $10.25   5.709%   $10.8352   $10.84   $10.85   $10.80  
  7 purchase totals = $702.64       $752.8831   $752.89   $752.90   $752.90