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 $78.37   6.828%   $83.7211   $83.72   $83.70   $83.70  
  Purchase #2 $152.35   5.392%   $160.5647   $160.56   $160.55   $160.60  
  Purchase #3 $204.82   7.116%   $219.395   $219.40   $219.40   $219.40  
  Purchase #4 $134.64   11.140%   $149.6389   $149.64   $149.65   $149.60  
  Purchase #5 $37.89   6.121%   $40.2092   $40.21   $40.20   $40.20  
  Purchase #6 $103.93   9.389%   $113.688   $113.69   $113.70   $113.70  
  Purchase #7 $239.27   9.825%   $262.7783   $262.78   $262.80   $262.80  
  7 purchase totals = $951.27       $1,029.9952   $1,030.00   $1,030.00   $1,030.00