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 $70.51   6.386%   $75.0128   $75.01   $75.00   $75.00  
  Purchase #2 $139.83   7.716%   $150.6193   $150.62   $150.60   $150.60  
  Purchase #3 $94.39   13.874%   $107.4857   $107.49   $107.50   $107.50  
  Purchase #4 $214.31   13.736%   $243.7476   $243.75   $243.75   $243.70  
  Purchase #5 $148.29   11.759%   $165.7274   $165.73   $165.75   $165.70  
  Purchase #6 $52.88   13.766%   $60.1595   $60.16   $60.15   $60.20  
  Purchase #7 $229.88   7.436%   $246.9739   $246.97   $246.95   $247.00  
  7 purchase totals = $950.09       $1,049.7262   $1,049.73   $1,049.70   $1,049.70