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 $179.85   13.278%   $203.7305   $203.73   $203.75   $203.70  
  Purchase #2 $25.53   6.505%   $27.1907   $27.19   $27.20   $27.20  
  Purchase #3 $84.82   8.555%   $92.0764   $92.08   $92.10   $92.10  
  Purchase #4 $32.33   7.578%   $34.78   $34.78   $34.80   $34.80  
  Purchase #5 $245.59   6.198%   $260.8117   $260.81   $260.80   $260.80  
  Purchase #6 $238.97   12.535%   $268.9249   $268.92   $268.90   $268.90  
  Purchase #7 $185.43   3.602%   $192.1092   $192.11   $192.10   $192.10  
  7 purchase totals = $992.52       $1,079.6234   $1,079.62   $1,079.65   $1,079.60