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 $53.91   12.548%   $60.6746   $60.67   $60.65   $60.70  
  Purchase #2 $132.94   11.132%   $147.7389   $147.74   $147.75   $147.70  
  Purchase #3 $129.63   11.255%   $144.2199   $144.22   $144.20   $144.20  
  Purchase #4 $126.42   3.830%   $131.2619   $131.26   $131.25   $131.30  
  Purchase #5 $228.49   10.134%   $251.6452   $251.65   $251.65   $251.60  
  Purchase #6 $162.79   10.194%   $179.3848   $179.38   $179.40   $179.40  
  Purchase #7 $145.92   4.179%   $152.018   $152.02   $152.00   $152.00  
  7 purchase totals = $980.10       $1,066.9433   $1,066.94   $1,066.90   $1,066.90