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 $24.50   8.229%   $26.5161   $26.52   $26.50   $26.50  
  Purchase #2 $197.92   9.360%   $216.4453   $216.45   $216.45   $216.40  
  Purchase #3 $167.93   9.561%   $183.9858   $183.99   $184.00   $184.00  
  Purchase #4 $235.75   12.174%   $264.4502   $264.45   $264.45   $264.50  
  Purchase #5 $174.36   6.385%   $185.4929   $185.49   $185.50   $185.50  
  Purchase #6 $29.78   13.565%   $33.8197   $33.82   $33.80   $33.80  
  Purchase #7 $27.79   11.606%   $31.0153   $31.02   $31.00   $31.00  
  7 purchase totals = $858.03       $941.7253   $941.74   $941.70   $941.70