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 $73.62   12.689%   $82.9616   $82.96   $82.95   $83.00  
  Purchase #2 $104.97   4.557%   $109.7535   $109.75   $109.75   $109.80  
  Purchase #3 $225.92   8.385%   $244.8634   $244.86   $244.85   $244.90  
  Purchase #4 $46.73   3.215%   $48.2324   $48.23   $48.25   $48.20  
  Purchase #5 $200.80   7.806%   $216.4744   $216.47   $216.45   $216.50  
  Purchase #6 $165.25   8.421%   $179.1657   $179.17   $179.15   $179.20  
  Purchase #7 $181.69   10.806%   $201.3234   $201.32   $201.30   $201.30  
  7 purchase totals = $998.98       $1,082.7744   $1,082.76   $1,082.70   $1,082.90