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 $202.81   11.407%   $225.9445   $225.94   $225.95   $225.90  
  Purchase #2 $161.28   3.623%   $167.1232   $167.12   $167.10   $167.10  
  Purchase #3 $42.56   8.775%   $46.2946   $46.29   $46.30   $46.30  
  Purchase #4 $162.97   6.802%   $174.0552   $174.06   $174.05   $174.10  
  Purchase #5 $99.84   13.757%   $113.575   $113.58   $113.60   $113.60  
  Purchase #6 $144.61   11.288%   $160.9336   $160.93   $160.95   $160.90  
  Purchase #7 $132.92   12.620%   $149.6945   $149.69   $149.70   $149.70  
  7 purchase totals = $946.99       $1,037.6206   $1,037.61   $1,037.65   $1,037.60