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 $248.98   9.562%   $272.7875   $272.79   $272.80   $272.80  
  Purchase #2 $24.99   10.175%   $27.5327   $27.53   $27.55   $27.50  
  Purchase #3 $73.66   9.180%   $80.422   $80.42   $80.40   $80.40  
  Purchase #4 $117.80   6.398%   $125.3368   $125.34   $125.35   $125.30  
  Purchase #5 $23.29   9.399%   $25.479   $25.48   $25.50   $25.50  
  Purchase #6 $101.84   6.559%   $108.5197   $108.52   $108.50   $108.50  
  Purchase #7 $60.74   8.385%   $65.833   $65.83   $65.85   $65.80  
  7 purchase totals = $651.30       $705.9107   $705.91   $705.95   $705.80