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 $240.31   9.563%   $263.2908   $263.29   $263.30   $263.30  
  Purchase #2 $124.37   5.496%   $131.2054   $131.21   $131.20   $131.20  
  Purchase #3 $183.97   7.146%   $197.1165   $197.12   $197.10   $197.10  
  Purchase #4 $94.67   9.343%   $103.515   $103.52   $103.50   $103.50  
  Purchase #5 $53.46   9.847%   $58.7242   $58.72   $58.70   $58.70  
  Purchase #6 $180.78   9.171%   $197.3593   $197.36   $197.35   $197.40  
  Purchase #7 $67.97   9.302%   $74.2926   $74.29   $74.30   $74.30  
  7 purchase totals = $945.53       $1,025.5038   $1,025.51   $1,025.45   $1,025.50