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 $59.38   8.753%   $64.5775   $64.58   $64.60   $64.60  
  Purchase #2 $191.31   6.266%   $203.2975   $203.30   $203.30   $203.30  
  Purchase #3 $94.45   8.874%   $102.8315   $102.83   $102.85   $102.80  
  Purchase #4 $5.47   5.590%   $5.7758   $5.78   $5.80   $5.80  
  Purchase #5 $93.91   3.546%   $97.24   $97.24   $97.25   $97.20  
  Purchase #6 $65.27   12.521%   $73.4425   $73.44   $73.45   $73.40  
  Purchase #7 $136.72   6.625%   $145.7777   $145.78   $145.80   $145.80  
  7 purchase totals = $646.51       $692.9425   $692.95   $693.05   $692.90