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 $82.56   7.457%   $88.7165   $88.72   $88.70   $88.70  
  Purchase #2 $212.90   11.293%   $236.9428   $236.94   $236.95   $236.90  
  Purchase #3 $133.43   13.558%   $151.5204   $151.52   $151.50   $151.50  
  Purchase #4 $171.67   7.518%   $184.5762   $184.58   $184.60   $184.60  
  Purchase #5 $179.45   7.856%   $193.5476   $193.55   $193.55   $193.50  
  Purchase #6 $212.66   5.367%   $224.0735   $224.07   $224.05   $224.10  
  Purchase #7 $166.80   7.632%   $179.5302   $179.53   $179.55   $179.50  
  7 purchase totals = $1,159.47       $1,258.9072   $1,258.91   $1,258.90   $1,258.80