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 $240.53   4.643%   $251.6978   $251.70   $251.70   $251.70  
  Purchase #2 $23.44   8.141%   $25.3483   $25.35   $25.35   $25.30  
  Purchase #3 $131.78   7.553%   $141.7333   $141.73   $141.75   $141.70  
  Purchase #4 $238.52   4.619%   $249.5372   $249.54   $249.55   $249.50  
  Purchase #5 $71.52   3.806%   $74.2421   $74.24   $74.25   $74.20  
  Purchase #6 $126.65   9.753%   $139.0022   $139.00   $139.00   $139.00  
  Purchase #7 $149.51   13.628%   $169.8852   $169.89   $169.90   $169.90  
  7 purchase totals = $981.95       $1,051.4461   $1,051.45   $1,051.50   $1,051.30