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 $7.50   4.700%   $7.8525   $7.85   $7.85   $7.90  
  Purchase #2 $20.29   4.692%   $21.242   $21.24   $21.25   $21.20  
  Purchase #3 $147.28   12.290%   $165.3807   $165.38   $165.40   $165.40  
  Purchase #4 $58.56   12.287%   $65.7553   $65.76   $65.75   $65.80  
  Purchase #5 $204.25   8.555%   $221.7236   $221.72   $221.70   $221.70  
  Purchase #6 $124.84   8.583%   $135.555   $135.56   $135.55   $135.60  
  Purchase #7 $73.34   6.133%   $77.8379   $77.84   $77.85   $77.80  
  7 purchase totals = $636.06       $695.3470   $695.35   $695.35   $695.40