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 $154.93   13.196%   $175.3746   $175.37   $175.35   $175.40  
  Purchase #2 $220.98   6.721%   $235.8321   $235.83   $235.85   $235.80  
  Purchase #3 $19.53   10.340%   $21.5494   $21.55   $21.55   $21.50  
  Purchase #4 $76.98   13.773%   $87.5825   $87.58   $87.60   $87.60  
  Purchase #5 $89.43   13.430%   $101.4404   $101.44   $101.45   $101.40  
  Purchase #6 $166.84   10.386%   $184.168   $184.17   $184.15   $184.20  
  Purchase #7 $236.81   8.277%   $256.4108   $256.41   $256.40   $256.40  
  7 purchase totals = $965.50       $1,062.3578   $1,062.35   $1,062.35   $1,062.30