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 $191.84   8.385%   $207.9258   $207.93   $207.95   $207.90  
  Purchase #2 $186.62   4.529%   $195.072   $195.07   $195.05   $195.10  
  Purchase #3 $74.63   5.594%   $78.8048   $78.80   $78.80   $78.80  
  Purchase #4 $93.36   8.592%   $101.3815   $101.38   $101.40   $101.40  
  Purchase #5 $212.81   4.828%   $223.0845   $223.08   $223.10   $223.10  
  Purchase #6 $150.92   12.823%   $170.2725   $170.27   $170.25   $170.30  
  Purchase #7 $75.89   7.597%   $81.6554   $81.66   $81.65   $81.70  
  7 purchase totals = $986.07       $1,058.1965   $1,058.19   $1,058.20   $1,058.30