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 $224.29   11.129%   $249.2512   $249.25   $249.25   $249.30  
  Purchase #2 $31.52   8.144%   $34.087   $34.09   $34.10   $34.10  
  Purchase #3 $87.41   11.812%   $97.7349   $97.73   $97.75   $97.70  
  Purchase #4 $169.67   8.160%   $183.5151   $183.52   $183.50   $183.50  
  Purchase #5 $133.72   12.579%   $150.5406   $150.54   $150.55   $150.50  
  Purchase #6 $181.34   12.753%   $204.4663   $204.47   $204.45   $204.50  
  Purchase #7 $127.97   8.661%   $139.0535   $139.05   $139.05   $139.10  
  7 purchase totals = $955.92       $1,058.6486   $1,058.65   $1,058.65   $1,058.70