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 $43.55   8.764%   $47.3667   $47.37   $47.35   $47.40  
  Purchase #2 $180.95   4.466%   $189.0312   $189.03   $189.05   $189.00  
  Purchase #3 $133.67   3.532%   $138.3912   $138.39   $138.40   $138.40  
  Purchase #4 $209.57   3.863%   $217.6657   $217.67   $217.65   $217.70  
  Purchase #5 $170.88   11.270%   $190.1382   $190.14   $190.15   $190.10  
  Purchase #6 $43.48   8.369%   $47.1188   $47.12   $47.10   $47.10  
  Purchase #7 $227.80   3.667%   $236.1534   $236.15   $236.15   $236.20  
  7 purchase totals = $1,009.90       $1,065.8652   $1,065.87   $1,065.85   $1,065.90