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 $106.47   11.218%   $118.4138   $118.41   $118.40   $118.40  
  Purchase #2 $234.96   13.369%   $266.3718   $266.37   $266.35   $266.40  
  Purchase #3 $205.31   13.690%   $233.4169   $233.42   $233.40   $233.40  
  Purchase #4 $231.67   6.173%   $245.971   $245.97   $245.95   $246.00  
  Purchase #5 $156.92   8.617%   $170.4418   $170.44   $170.45   $170.40  
  Purchase #6 $87.44   8.107%   $94.5288   $94.53   $94.55   $94.50  
  Purchase #7 $151.69   9.248%   $165.7183   $165.72   $165.70   $165.70  
  7 purchase totals = $1,174.46       $1,294.8624   $1,294.86   $1,294.80   $1,294.80