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 $32.76   10.220%   $36.1081   $36.11   $36.10   $36.10  
  Purchase #2 $95.69   6.704%   $102.1051   $102.11   $102.10   $102.10  
  Purchase #3 $137.56   10.810%   $152.4302   $152.43   $152.45   $152.40  
  Purchase #4 $216.61   9.462%   $237.1056   $237.11   $237.10   $237.10  
  Purchase #5 $187.99   11.518%   $209.6427   $209.64   $209.65   $209.60  
  Purchase #6 $48.32   11.495%   $53.8744   $53.87   $53.85   $53.90  
  Purchase #7 $214.82   7.123%   $230.1216   $230.12   $230.10   $230.10  
  7 purchase totals = $933.75       $1,021.3877   $1,021.39   $1,021.35   $1,021.30