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 $136.82   11.145%   $152.0686   $152.07   $152.05   $152.10  
  Purchase #2 $62.89   6.198%   $66.7879   $66.79   $66.80   $66.80  
  Purchase #3 $189.61   9.444%   $207.5168   $207.52   $207.50   $207.50  
  Purchase #4 $228.66   6.469%   $243.452   $243.45   $243.45   $243.50  
  Purchase #5 $109.58   5.559%   $115.6716   $115.67   $115.65   $115.70  
  Purchase #6 $235.60   3.861%   $244.6965   $244.70   $244.70   $244.70  
  Purchase #7 $28.96   6.285%   $30.7801   $30.78   $30.80   $30.80  
  7 purchase totals = $992.12       $1,060.9735   $1,060.98   $1,060.95   $1,061.10