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 $181.96   11.436%   $202.7689   $202.77   $202.75   $202.80  
  Purchase #2 $25.59   5.469%   $26.9895   $26.99   $27.00   $27.00  
  Purchase #3 $113.29   12.273%   $127.1941   $127.19   $127.20   $127.20  
  Purchase #4 $241.33   12.574%   $271.6748   $271.67   $271.65   $271.70  
  Purchase #5 $129.50   11.676%   $144.6204   $144.62   $144.60   $144.60  
  Purchase #6 $142.43   12.408%   $160.1027   $160.10   $160.10   $160.10  
  Purchase #7 $176.95   4.468%   $184.8561   $184.86   $184.85   $184.90  
  7 purchase totals = $1,011.05       $1,118.2065   $1,118.20   $1,118.15   $1,118.30