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 $46.60   10.780%   $51.6235   $51.62   $51.60   $51.60  
  Purchase #2 $144.51   4.579%   $151.1271   $151.13   $151.15   $151.10  
  Purchase #3 $186.64   9.586%   $204.5313   $204.53   $204.55   $204.50  
  Purchase #4 $211.46   4.661%   $221.3162   $221.32   $221.30   $221.30  
  Purchase #5 $128.87   7.520%   $138.561   $138.56   $138.55   $138.60  
  Purchase #6 $34.54   3.550%   $35.7662   $35.77   $35.75   $35.80  
  Purchase #7 $202.61   4.468%   $211.6626   $211.66   $211.65   $211.70  
  7 purchase totals = $955.23       $1,014.5879   $1,014.59   $1,014.55   $1,014.60