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 $231.38   12.693%   $260.7491   $260.75   $260.75   $260.70  
  Purchase #2 $244.45   13.461%   $277.3554   $277.36   $277.35   $277.40  
  Purchase #3 $159.64   9.841%   $175.3502   $175.35   $175.35   $175.40  
  Purchase #4 $15.48   6.206%   $16.4407   $16.44   $16.45   $16.40  
  Purchase #5 $216.66   13.118%   $245.0815   $245.08   $245.10   $245.10  
  Purchase #6 $90.27   3.271%   $93.2227   $93.22   $93.20   $93.20  
  Purchase #7 $7.94   4.647%   $8.309   $8.31   $8.30   $8.30  
  7 purchase totals = $965.82       $1,076.5086   $1,076.51   $1,076.50   $1,076.50