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 $141.45   13.506%   $160.5542   $160.55   $160.55   $160.60  
  Purchase #2 $53.38   10.202%   $58.8258   $58.83   $58.85   $58.80  
  Purchase #3 $221.65   6.197%   $235.3857   $235.39   $235.40   $235.40  
  Purchase #4 $115.82   9.366%   $126.6677   $126.67   $126.65   $126.70  
  Purchase #5 $210.46   13.140%   $238.1144   $238.11   $238.10   $238.10  
  Purchase #6 $238.52   6.762%   $254.6487   $254.65   $254.65   $254.60  
  Purchase #7 $68.44   5.718%   $72.3534   $72.35   $72.35   $72.40  
  7 purchase totals = $1,049.72       $1,146.5499   $1,146.55   $1,146.55   $1,146.60