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 $50.91   11.365%   $56.6959   $56.70   $56.70   $56.70  
  Purchase #2 $181.66   13.377%   $205.9607   $205.96   $205.95   $206.00  
  Purchase #3 $39.32   10.494%   $43.4462   $43.45   $43.45   $43.40  
  Purchase #4 $12.59   13.471%   $14.286   $14.29   $14.30   $14.30  
  Purchase #5 $65.33   5.433%   $68.8794   $68.88   $68.90   $68.90  
  Purchase #6 $195.67   11.572%   $218.3129   $218.31   $218.30   $218.30  
  Purchase #7 $173.99   13.238%   $197.0228   $197.02   $197.00   $197.00  
  7 purchase totals = $719.47       $804.6039   $804.61   $804.60   $804.60