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 $85.84   13.763%   $97.6542   $97.65   $97.65   $97.70  
  Purchase #2 $241.55   12.358%   $271.4007   $271.40   $271.40   $271.40  
  Purchase #3 $219.40   12.409%   $246.6253   $246.63   $246.65   $246.60  
  Purchase #4 $204.48   7.638%   $220.0982   $220.10   $220.10   $220.10  
  Purchase #5 $98.29   12.361%   $110.4396   $110.44   $110.45   $110.40  
  Purchase #6 $107.87   6.436%   $114.8125   $114.81   $114.80   $114.80  
  Purchase #7 $27.70   12.766%   $31.2362   $31.24   $31.25   $31.20  
  7 purchase totals = $985.13       $1,092.2667   $1,092.27   $1,092.30   $1,092.20