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 $200.99   7.544%   $216.1527   $216.15   $216.15   $216.20  
  Purchase #2 $245.57   9.230%   $268.2361   $268.24   $268.25   $268.20  
  Purchase #3 $217.32   13.656%   $246.9972   $247.00   $247.00   $247.00  
  Purchase #4 $103.97   13.552%   $118.06   $118.06   $118.05   $118.10  
  Purchase #5 $128.74   8.549%   $139.746   $139.75   $139.75   $139.70  
  Purchase #6 $74.48   12.731%   $83.962   $83.96   $83.95   $84.00  
  Purchase #7 $70.78   13.171%   $80.1024   $80.10   $80.10   $80.10  
  7 purchase totals = $1,041.85       $1,153.2564   $1,153.26   $1,153.25   $1,153.30