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 $57.50   3.644%   $59.5953   $59.60   $59.60   $59.60  
  Purchase #2 $98.66   12.319%   $110.8139   $110.81   $110.80   $110.80  
  Purchase #3 $232.27   5.392%   $244.794   $244.79   $244.80   $244.80  
  Purchase #4 $97.80   9.698%   $107.2846   $107.28   $107.30   $107.30  
  Purchase #5 $218.51   13.712%   $248.4721   $248.47   $248.45   $248.50  
  Purchase #6 $149.57   12.239%   $167.8759   $167.88   $167.90   $167.90  
  Purchase #7 $160.96   12.176%   $180.5585   $180.56   $180.55   $180.60  
  7 purchase totals = $1,015.27       $1,119.3943   $1,119.39   $1,119.40   $1,119.50