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 $69.72   10.674%   $77.1619   $77.16   $77.15   $77.20  
  Purchase #2 $87.44   13.735%   $99.4499   $99.45   $99.45   $99.40  
  Purchase #3 $216.82   4.873%   $227.3856   $227.39   $227.40   $227.40  
  Purchase #4 $201.79   4.840%   $211.5566   $211.56   $211.55   $211.60  
  Purchase #5 $154.46   4.667%   $161.6686   $161.67   $161.65   $161.70  
  Purchase #6 $203.60   6.530%   $216.8951   $216.90   $216.90   $216.90  
  Purchase #7 $10.31   12.564%   $11.6053   $11.61   $11.60   $11.60  
  7 purchase totals = $944.14       $1,005.7230   $1,005.74   $1,005.70   $1,005.80