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 $58.96   13.707%   $67.0416   $67.04   $67.05   $67.00  
  Purchase #2 $172.43   9.580%   $188.9488   $188.95   $188.95   $188.90  
  Purchase #3 $222.88   8.812%   $242.5202   $242.52   $242.50   $242.50  
  Purchase #4 $138.91   8.120%   $150.1895   $150.19   $150.20   $150.20  
  Purchase #5 $185.70   13.150%   $210.1196   $210.12   $210.10   $210.10  
  Purchase #6 $186.44   9.787%   $204.6869   $204.69   $204.70   $204.70  
  Purchase #7 $201.89   8.137%   $218.3178   $218.32   $218.30   $218.30  
  7 purchase totals = $1,167.21       $1,281.8244   $1,281.83   $1,281.80   $1,281.70