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 $118.88   10.197%   $131.0022   $131.00   $131.00   $131.00  
  Purchase #2 $28.30   8.211%   $30.6237   $30.62   $30.60   $30.60  
  Purchase #3 $219.65   11.409%   $244.7099   $244.71   $244.70   $244.70  
  Purchase #4 $105.58   11.587%   $117.8136   $117.81   $117.80   $117.80  
  Purchase #5 $88.42   9.668%   $96.9684   $96.97   $96.95   $97.00  
  Purchase #6 $228.94   13.189%   $259.1349   $259.13   $259.15   $259.10  
  Purchase #7 $160.26   12.790%   $180.7573   $180.76   $180.75   $180.80  
  7 purchase totals = $950.03       $1,061.0100   $1,061.00   $1,060.95   $1,061.00