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 $66.65   10.580%   $73.7016   $73.70   $73.70   $73.70  
  Purchase #2 $109.43   9.677%   $120.0195   $120.02   $120.00   $120.00  
  Purchase #3 $146.74   10.740%   $162.4999   $162.50   $162.50   $162.50  
  Purchase #4 $203.77   12.820%   $229.8933   $229.89   $229.90   $229.90  
  Purchase #5 $227.71   11.237%   $253.2978   $253.30   $253.30   $253.30  
  Purchase #6 $25.35   4.760%   $26.5567   $26.56   $26.55   $26.60  
  Purchase #7 $206.29   6.591%   $219.8866   $219.89   $219.90   $219.90  
  7 purchase totals = $985.94       $1,085.8554   $1,085.86   $1,085.85   $1,085.90