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 $116.42   13.323%   $131.9306   $131.93   $131.95   $131.90  
  Purchase #2 $227.53   11.488%   $253.6686   $253.67   $253.65   $253.70  
  Purchase #3 $99.73   7.247%   $106.9574   $106.96   $106.95   $107.00  
  Purchase #4 $201.30   6.711%   $214.8092   $214.81   $214.80   $214.80  
  Purchase #5 $36.81   4.759%   $38.5618   $38.56   $38.55   $38.60  
  Purchase #6 $155.42   6.636%   $165.7337   $165.73   $165.75   $165.70  
  Purchase #7 $107.32   11.261%   $119.4053   $119.41   $119.40   $119.40  
  7 purchase totals = $944.53       $1,031.0666   $1,031.07   $1,031.05   $1,031.10