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 $188.69   7.691%   $203.2021   $203.20   $203.20   $203.20  
  Purchase #2 $65.43   6.121%   $69.435   $69.44   $69.45   $69.40  
  Purchase #3 $165.85   6.823%   $177.1659   $177.17   $177.15   $177.20  
  Purchase #4 $52.62   4.299%   $54.8821   $54.88   $54.90   $54.90  
  Purchase #5 $47.60   4.839%   $49.9034   $49.90   $49.90   $49.90  
  Purchase #6 $145.26   5.703%   $153.5442   $153.54   $153.55   $153.50  
  Purchase #7 $42.27   7.258%   $45.338   $45.34   $45.35   $45.30  
  7 purchase totals = $707.72       $753.4707   $753.47   $753.50   $753.40