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 $59.27   4.418%   $61.8885   $61.89   $61.90   $61.90  
  Purchase #2 $198.94   11.349%   $221.5177   $221.52   $221.50   $221.50  
  Purchase #3 $30.43   3.142%   $31.3861   $31.39   $31.40   $31.40  
  Purchase #4 $155.51   6.103%   $165.0008   $165.00   $165.00   $165.00  
  Purchase #5 $84.79   10.417%   $93.6226   $93.62   $93.60   $93.60  
  Purchase #6 $27.48   13.485%   $31.1857   $31.19   $31.20   $31.20  
  Purchase #7 $225.82   6.755%   $241.0741   $241.07   $241.05   $241.10  
  7 purchase totals = $782.24       $845.6755   $845.68   $845.65   $845.70