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 $208.55   12.145%   $233.8784   $233.88   $233.90   $233.90  
  Purchase #2 $108.53   11.167%   $120.6495   $120.65   $120.65   $120.60  
  Purchase #3 $11.28   6.190%   $11.9782   $11.98   $12.00   $12.00  
  Purchase #4 $191.99   8.194%   $207.7217   $207.72   $207.70   $207.70  
  Purchase #5 $97.50   13.802%   $110.957   $110.96   $110.95   $111.00  
  Purchase #6 $219.26   13.647%   $249.1824   $249.18   $249.20   $249.20  
  Purchase #7 $229.81   4.851%   $240.9581   $240.96   $240.95   $241.00  
  7 purchase totals = $1,066.92       $1,175.3253   $1,175.33   $1,175.35   $1,175.40