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 $53.94   9.347%   $58.9818   $58.98   $59.00   $59.00  
  Purchase #2 $177.99   7.323%   $191.0242   $191.02   $191.00   $191.00  
  Purchase #3 $213.45   3.272%   $220.4341   $220.43   $220.45   $220.40  
  Purchase #4 $71.73   4.648%   $75.064   $75.06   $75.05   $75.10  
  Purchase #5 $63.35   11.802%   $70.8266   $70.83   $70.85   $70.80  
  Purchase #6 $175.95   4.213%   $183.3628   $183.36   $183.35   $183.40  
  Purchase #7 $232.54   10.666%   $257.3427   $257.34   $257.35   $257.30  
  7 purchase totals = $988.95       $1,057.0362   $1,057.02   $1,057.05   $1,057.00