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 $191.78   5.508%   $202.3432   $202.34   $202.35   $202.30  
  Purchase #2 $167.52   3.235%   $172.9393   $172.94   $172.95   $172.90  
  Purchase #3 $56.37   11.706%   $62.9687   $62.97   $62.95   $63.00  
  Purchase #4 $106.40   9.270%   $116.2633   $116.26   $116.25   $116.30  
  Purchase #5 $139.98   13.297%   $158.5931   $158.59   $158.60   $158.60  
  Purchase #6 $241.33   3.661%   $250.1651   $250.17   $250.15   $250.20  
  Purchase #7 $5.62   12.765%   $6.3374   $6.34   $6.35   $6.30  
  7 purchase totals = $909.00       $969.6101   $969.61   $969.60   $969.60