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 $242.53   8.421%   $262.9535   $262.95   $262.95   $263.00  
  Purchase #2 $59.61   4.484%   $62.2829   $62.28   $62.30   $62.30  
  Purchase #3 $194.67   9.404%   $212.9768   $212.98   $213.00   $213.00  
  Purchase #4 $242.80   11.201%   $269.996   $270.00   $270.00   $270.00  
  Purchase #5 $124.51   5.774%   $131.6992   $131.70   $131.70   $131.70  
  Purchase #6 $242.52   8.159%   $262.3072   $262.31   $262.30   $262.30  
  Purchase #7 $197.61   12.456%   $222.2243   $222.22   $222.20   $222.20  
  7 purchase totals = $1,304.25       $1,424.4399   $1,424.44   $1,424.45   $1,424.50