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 $52.65   13.832%   $59.9325   $59.93   $59.95   $59.90  
  Purchase #2 $128.35   6.466%   $136.6491   $136.65   $136.65   $136.60  
  Purchase #3 $83.44   12.166%   $93.5913   $93.59   $93.60   $93.60  
  Purchase #4 $50.56   8.263%   $54.7378   $54.74   $54.75   $54.70  
  Purchase #5 $22.48   10.385%   $24.8145   $24.81   $24.80   $24.80  
  Purchase #6 $246.98   9.630%   $270.7642   $270.76   $270.75   $270.80  
  Purchase #7 $226.33   6.679%   $241.4466   $241.45   $241.45   $241.40  
  7 purchase totals = $810.79       $881.9360   $881.93   $881.95   $881.80