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 $204.93   3.458%   $212.0165   $212.02   $212.00   $212.00  
  Purchase #2 $39.47   4.635%   $41.2994   $41.30   $41.30   $41.30  
  Purchase #3 $77.41   7.649%   $83.3311   $83.33   $83.35   $83.30  
  Purchase #4 $122.44   3.300%   $126.4805   $126.48   $126.50   $126.50  
  Purchase #5 $247.62   8.350%   $268.2963   $268.30   $268.30   $268.30  
  Purchase #6 $233.27   5.279%   $245.5843   $245.58   $245.60   $245.60  
  Purchase #7 $65.59   8.827%   $71.3796   $71.38   $71.40   $71.40  
  7 purchase totals = $990.73       $1,048.3877   $1,048.39   $1,048.45   $1,048.40