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 $79.48   8.341%   $86.1094   $86.11   $86.10   $86.10  
  Purchase #2 $150.94   9.391%   $165.1148   $165.11   $165.10   $165.10  
  Purchase #3 $120.71   6.674%   $128.7662   $128.77   $128.75   $128.80  
  Purchase #4 $239.54   4.498%   $250.3145   $250.31   $250.30   $250.30  
  Purchase #5 $239.45   10.478%   $264.5396   $264.54   $264.55   $264.50  
  Purchase #6 $118.89   6.482%   $126.5964   $126.60   $126.60   $126.60  
  Purchase #7 $210.48   12.869%   $237.5667   $237.57   $237.55   $237.60  
  7 purchase totals = $1,159.49       $1,259.0076   $1,259.01   $1,258.95   $1,259.00