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 $58.98   3.564%   $61.082   $61.08   $61.10   $61.10  
  Purchase #2 $88.68   13.253%   $100.4328   $100.43   $100.45   $100.40  
  Purchase #3 $207.71   5.796%   $219.7489   $219.75   $219.75   $219.70  
  Purchase #4 $151.66   7.145%   $162.4961   $162.50   $162.50   $162.50  
  Purchase #5 $124.66   6.401%   $132.6395   $132.64   $132.65   $132.60  
  Purchase #6 $244.58   6.640%   $260.8201   $260.82   $260.80   $260.80  
  Purchase #7 $120.51   10.769%   $133.4877   $133.49   $133.50   $133.50  
  7 purchase totals = $996.78       $1,070.7071   $1,070.71   $1,070.75   $1,070.60