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 $84.62   7.596%   $91.0477   $91.05   $91.05   $91.00  
  Purchase #2 $196.30   5.289%   $206.6823   $206.68   $206.70   $206.70  
  Purchase #3 $241.31   9.542%   $264.3358   $264.34   $264.35   $264.30  
  Purchase #4 $62.32   10.313%   $68.7471   $68.75   $68.75   $68.70  
  Purchase #5 $51.57   12.210%   $57.8667   $57.87   $57.85   $57.90  
  Purchase #6 $26.58   6.306%   $28.2561   $28.26   $28.25   $28.30  
  Purchase #7 $99.93   9.332%   $109.2555   $109.26   $109.25   $109.30  
  7 purchase totals = $762.63       $826.1912   $826.21   $826.20   $826.20