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 $204.58   5.731%   $216.3045   $216.30   $216.30   $216.30  
  Purchase #2 $179.70   12.535%   $202.2254   $202.23   $202.25   $202.20  
  Purchase #3 $77.86   5.185%   $81.897   $81.90   $81.90   $81.90  
  Purchase #4 $118.64   8.656%   $128.9095   $128.91   $128.90   $128.90  
  Purchase #5 $73.36   11.751%   $81.9805   $81.98   $82.00   $82.00  
  Purchase #6 $190.77   5.586%   $201.4264   $201.43   $201.45   $201.40  
  Purchase #7 $95.34   9.257%   $104.1656   $104.17   $104.15   $104.20  
  7 purchase totals = $940.25       $1,016.9089   $1,016.92   $1,016.95   $1,016.90