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 $75.52   11.174%   $83.9586   $83.96   $83.95   $84.00  
  Purchase #2 $127.36   9.632%   $139.6273   $139.63   $139.65   $139.60  
  Purchase #3 $232.46   5.107%   $244.3317   $244.33   $244.35   $244.30  
  Purchase #4 $218.85   3.685%   $226.9146   $226.91   $226.90   $226.90  
  Purchase #5 $147.91   12.289%   $166.0867   $166.09   $166.10   $166.10  
  Purchase #6 $190.68   6.795%   $203.6367   $203.64   $203.65   $203.60  
  Purchase #7 $37.65   7.125%   $40.3326   $40.33   $40.35   $40.30  
  7 purchase totals = $1,030.43       $1,104.8882   $1,104.89   $1,104.95   $1,104.80