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 $141.52   10.824%   $156.8381   $156.84   $156.85   $156.80  
  Purchase #2 $104.78   11.653%   $116.99   $116.99   $117.00   $117.00  
  Purchase #3 $5.59   10.862%   $6.1972   $6.20   $6.20   $6.20  
  Purchase #4 $32.54   10.591%   $35.9863   $35.99   $36.00   $36.00  
  Purchase #5 $160.91   6.848%   $171.9291   $171.93   $171.95   $171.90  
  Purchase #6 $205.69   6.573%   $219.21   $219.21   $219.20   $219.20  
  Purchase #7 $180.76   13.281%   $204.7667   $204.77   $204.75   $204.80  
  7 purchase totals = $831.79       $911.9174   $911.93   $911.95   $911.90