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 $82.82   6.275%   $88.017   $88.02   $88.00   $88.00  
  Purchase #2 $151.26   9.168%   $165.1275   $165.13   $165.15   $165.10  
  Purchase #3 $83.68   4.577%   $87.51   $87.51   $87.50   $87.50  
  Purchase #4 $65.35   5.358%   $68.8515   $68.85   $68.85   $68.90  
  Purchase #5 $60.75   12.563%   $68.382   $68.38   $68.40   $68.40  
  Purchase #6 $216.52   12.381%   $243.3273   $243.33   $243.35   $243.30  
  Purchase #7 $20.42   5.194%   $21.4806   $21.48   $21.50   $21.50  
  7 purchase totals = $680.80       $742.6959   $742.70   $742.75   $742.70