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 $210.29   10.204%   $231.748   $231.75   $231.75   $231.70  
  Purchase #2 $24.37   4.577%   $25.4854   $25.49   $25.50   $25.50  
  Purchase #3 $100.93   6.707%   $107.6994   $107.70   $107.70   $107.70  
  Purchase #4 $145.71   4.826%   $152.742   $152.74   $152.75   $152.70  
  Purchase #5 $39.85   13.163%   $45.0955   $45.10   $45.10   $45.10  
  Purchase #6 $55.29   9.163%   $60.3562   $60.36   $60.35   $60.40  
  Purchase #7 $169.53   13.160%   $191.8401   $191.84   $191.85   $191.80  
  7 purchase totals = $745.97       $814.9666   $814.98   $815.00   $814.90