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 $107.78   5.334%   $113.529   $113.53   $113.55   $113.50  
  Purchase #2 $158.98   11.110%   $176.6427   $176.64   $176.65   $176.60  
  Purchase #3 $186.87   8.699%   $203.1258   $203.13   $203.15   $203.10  
  Purchase #4 $170.99   11.603%   $190.83   $190.83   $190.85   $190.80  
  Purchase #5 $204.78   7.260%   $219.647   $219.65   $219.65   $219.60  
  Purchase #6 $41.32   8.274%   $44.7388   $44.74   $44.75   $44.70  
  Purchase #7 $67.62   3.279%   $69.8373   $69.84   $69.85   $69.80  
  7 purchase totals = $938.34       $1,018.3506   $1,018.36   $1,018.45   $1,018.10