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 $225.96   10.647%   $250.018   $250.02   $250.00   $250.00  
  Purchase #2 $181.69   5.290%   $191.3014   $191.30   $191.30   $191.30  
  Purchase #3 $218.73   3.776%   $226.9892   $226.99   $227.00   $227.00  
  Purchase #4 $170.90   9.547%   $187.2158   $187.22   $187.20   $187.20  
  Purchase #5 $165.58   8.830%   $180.2007   $180.20   $180.20   $180.20  
  Purchase #6 $184.53   9.251%   $201.6009   $201.60   $201.60   $201.60  
  Purchase #7 $104.81   5.400%   $110.4697   $110.47   $110.45   $110.50  
  7 purchase totals = $1,252.20       $1,347.7957   $1,347.80   $1,347.75   $1,347.80