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 $97.90   4.429%   $102.236   $102.24   $102.25   $102.20  
  Purchase #2 $104.90   6.770%   $112.0017   $112.00   $112.00   $112.00  
  Purchase #3 $225.45   4.625%   $235.8771   $235.88   $235.90   $235.90  
  Purchase #4 $81.38   12.610%   $91.642   $91.64   $91.65   $91.60  
  Purchase #5 $65.90   11.151%   $73.2485   $73.25   $73.25   $73.20  
  Purchase #6 $165.98   11.304%   $184.7424   $184.74   $184.75   $184.70  
  Purchase #7 $244.98   12.497%   $275.5952   $275.60   $275.60   $275.60  
  7 purchase totals = $986.49       $1,075.3429   $1,075.35   $1,075.40   $1,075.20