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 $181.78   13.302%   $205.9604   $205.96   $205.95   $206.00  
  Purchase #2 $100.34   6.590%   $106.9524   $106.95   $106.95   $107.00  
  Purchase #3 $86.90   7.793%   $93.6721   $93.67   $93.65   $93.70  
  Purchase #4 $56.40   3.688%   $58.48   $58.48   $58.50   $58.50  
  Purchase #5 $179.49   11.865%   $200.7865   $200.79   $200.80   $200.80  
  Purchase #6 $57.30   8.304%   $62.0582   $62.06   $62.05   $62.10  
  Purchase #7 $173.63   3.166%   $179.1271   $179.13   $179.15   $179.10  
  7 purchase totals = $835.84       $907.0367   $907.04   $907.05   $907.20