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 $61.57   12.415%   $69.2139   $69.21   $69.20   $69.20  
  Purchase #2 $181.38   13.497%   $205.8609   $205.86   $205.85   $205.90  
  Purchase #3 $101.90   4.638%   $106.6261   $106.63   $106.65   $106.60  
  Purchase #4 $141.63   12.741%   $159.6751   $159.68   $159.70   $159.70  
  Purchase #5 $130.91   5.766%   $138.4583   $138.46   $138.45   $138.50  
  Purchase #6 $226.34   6.151%   $240.2622   $240.26   $240.25   $240.30  
  Purchase #7 $152.80   12.743%   $172.2713   $172.27   $172.25   $172.30  
  7 purchase totals = $996.53       $1,092.3678   $1,092.37   $1,092.35   $1,092.50