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 $231.71   5.446%   $244.3289   $244.33   $244.35   $244.30  
  Purchase #2 $73.72   12.497%   $82.9328   $82.93   $82.95   $82.90  
  Purchase #3 $51.37   9.427%   $56.2126   $56.21   $56.20   $56.20  
  Purchase #4 $88.52   6.730%   $94.4774   $94.48   $94.50   $94.50  
  Purchase #5 $229.91   10.466%   $253.9724   $253.97   $253.95   $254.00  
  Purchase #6 $218.51   4.729%   $228.8433   $228.84   $228.85   $228.80  
  Purchase #7 $59.29   12.711%   $66.8264   $66.83   $66.85   $66.80  
  7 purchase totals = $953.03       $1,027.5938   $1,027.59   $1,027.65   $1,027.50