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 $225.71   9.196%   $246.4663   $246.47   $246.45   $246.50  
  Purchase #2 $53.30   11.318%   $59.3325   $59.33   $59.35   $59.30  
  Purchase #3 $233.75   4.122%   $243.3852   $243.39   $243.40   $243.40  
  Purchase #4 $86.62   12.449%   $97.4033   $97.40   $97.40   $97.40  
  Purchase #5 $65.29   5.150%   $68.6524   $68.65   $68.65   $68.70  
  Purchase #6 $141.97   10.303%   $156.5972   $156.60   $156.60   $156.60  
  Purchase #7 $219.70   5.697%   $232.2163   $232.22   $232.20   $232.20  
  7 purchase totals = $1,026.34       $1,104.0532   $1,104.06   $1,104.05   $1,104.10