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 $118.34   3.506%   $122.489   $122.49   $122.50   $122.50  
  Purchase #2 $178.71   11.157%   $198.6487   $198.65   $198.65   $198.60  
  Purchase #3 $140.56   6.690%   $149.9635   $149.96   $149.95   $150.00  
  Purchase #4 $191.36   6.549%   $203.8922   $203.89   $203.90   $203.90  
  Purchase #5 $59.92   11.596%   $66.8683   $66.87   $66.85   $66.90  
  Purchase #6 $202.54   13.807%   $230.5047   $230.50   $230.50   $230.50  
  Purchase #7 $55.95   7.443%   $60.1144   $60.11   $60.10   $60.10  
  7 purchase totals = $947.38       $1,032.4808   $1,032.47   $1,032.45   $1,032.50