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 $46.97   12.642%   $52.9079   $52.91   $52.90   $52.90  
  Purchase #2 $97.58   4.659%   $102.1263   $102.13   $102.15   $102.10  
  Purchase #3 $140.77   9.251%   $153.7926   $153.79   $153.80   $153.80  
  Purchase #4 $219.92   9.592%   $241.0147   $241.01   $241.00   $241.00  
  Purchase #5 $128.48   11.863%   $143.7216   $143.72   $143.70   $143.70  
  Purchase #6 $195.59   6.486%   $208.276   $208.28   $208.30   $208.30  
  Purchase #7 $178.97   7.227%   $191.9042   $191.90   $191.90   $191.90  
  7 purchase totals = $1,008.28       $1,093.7433   $1,093.74   $1,093.75   $1,093.70