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 $23.94   11.701%   $26.7412   $26.74   $26.75   $26.70  
  Purchase #2 $73.82   9.513%   $80.8425   $80.84   $80.85   $80.80  
  Purchase #3 $180.30   13.697%   $204.9957   $205.00   $205.00   $205.00  
  Purchase #4 $54.29   8.561%   $58.9378   $58.94   $58.95   $58.90  
  Purchase #5 $145.99   11.142%   $162.2562   $162.26   $162.25   $162.30  
  Purchase #6 $142.40   4.339%   $148.5787   $148.58   $148.60   $148.60  
  Purchase #7 $80.74   9.631%   $88.5161   $88.52   $88.50   $88.50  
  7 purchase totals = $701.48       $770.8682   $770.88   $770.90   $770.80