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 $54.88   11.120%   $60.9827   $60.98   $61.00   $61.00  
  Purchase #2 $239.52   7.195%   $256.7535   $256.75   $256.75   $256.80  
  Purchase #3 $57.50   11.622%   $64.1827   $64.18   $64.20   $64.20  
  Purchase #4 $70.95   9.277%   $77.532   $77.53   $77.55   $77.50  
  Purchase #5 $59.62   12.471%   $67.0552   $67.06   $67.05   $67.10  
  Purchase #6 $65.55   11.862%   $73.3255   $73.33   $73.35   $73.30  
  Purchase #7 $157.36   6.706%   $167.9126   $167.91   $167.90   $167.90  
  7 purchase totals = $705.38       $767.7442   $767.74   $767.80   $767.80