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 $64.95   11.360%   $72.3283   $72.33   $72.35   $72.30  
  Purchase #2 $232.53   3.783%   $241.3266   $241.33   $241.35   $241.30  
  Purchase #3 $90.89   4.814%   $95.2654   $95.27   $95.25   $95.30  
  Purchase #4 $145.89   11.133%   $162.1319   $162.13   $162.15   $162.10  
  Purchase #5 $227.74   10.294%   $251.1836   $251.18   $251.20   $251.20  
  Purchase #6 $191.98   5.383%   $202.3143   $202.31   $202.30   $202.30  
  Purchase #7 $51.36   12.539%   $57.8   $57.80   $57.80   $57.80  
  7 purchase totals = $1,005.34       $1,082.3501   $1,082.35   $1,082.40   $1,082.30