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 $219.86   6.136%   $233.3506   $233.35   $233.35   $233.40  
  Purchase #2 $232.30   13.140%   $262.8242   $262.82   $262.80   $262.80  
  Purchase #3 $102.97   7.394%   $110.5836   $110.58   $110.60   $110.60  
  Purchase #4 $209.76   9.835%   $230.3899   $230.39   $230.40   $230.40  
  Purchase #5 $69.57   5.853%   $73.6419   $73.64   $73.65   $73.60  
  Purchase #6 $14.91   8.815%   $16.2243   $16.22   $16.20   $16.20  
  Purchase #7 $203.51   8.399%   $220.6028   $220.60   $220.60   $220.60  
  7 purchase totals = $1,052.88       $1,147.6173   $1,147.60   $1,147.60   $1,147.60