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 $83.96   12.716%   $94.6364   $94.64   $94.65   $94.60  
  Purchase #2 $138.56   4.107%   $144.2507   $144.25   $144.25   $144.30  
  Purchase #3 $169.77   12.850%   $191.5854   $191.59   $191.60   $191.60  
  Purchase #4 $191.62   13.275%   $217.0576   $217.06   $217.05   $217.10  
  Purchase #5 $83.51   11.583%   $93.183   $93.18   $93.20   $93.20  
  Purchase #6 $206.79   6.136%   $219.4786   $219.48   $219.50   $219.50  
  Purchase #7 $55.34   5.787%   $58.5425   $58.54   $58.55   $58.50  
  7 purchase totals = $929.55       $1,018.7342   $1,018.74   $1,018.80   $1,018.80