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 $29.71   9.759%   $32.6094   $32.61   $32.60   $32.60  
  Purchase #2 $192.61   9.568%   $211.0389   $211.04   $211.05   $211.00  
  Purchase #3 $221.98   6.616%   $236.6662   $236.67   $236.65   $236.70  
  Purchase #4 $53.56   3.614%   $55.4957   $55.50   $55.50   $55.50  
  Purchase #5 $5.98   11.782%   $6.6846   $6.68   $6.70   $6.70  
  Purchase #6 $183.93   7.723%   $198.1349   $198.13   $198.15   $198.10  
  Purchase #7 $148.53   3.577%   $153.8429   $153.84   $153.85   $153.80  
  7 purchase totals = $836.30       $894.4726   $894.47   $894.50   $894.40