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 $200.61   12.710%   $226.1075   $226.11   $226.10   $226.10  
  Purchase #2 $31.87   13.618%   $36.2101   $36.21   $36.20   $36.20  
  Purchase #3 $77.33   11.519%   $86.2376   $86.24   $86.25   $86.20  
  Purchase #4 $67.77   11.723%   $75.7147   $75.71   $75.70   $75.70  
  Purchase #5 $166.93   10.290%   $184.1071   $184.11   $184.10   $184.10  
  Purchase #6 $40.65   6.802%   $43.415   $43.42   $43.40   $43.40  
  Purchase #7 $203.98   3.170%   $210.4462   $210.45   $210.45   $210.40  
  7 purchase totals = $789.14       $862.2382   $862.25   $862.20   $862.10