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 $184.97   13.152%   $209.2973   $209.30   $209.30   $209.30  
  Purchase #2 $236.97   7.210%   $254.0555   $254.06   $254.05   $254.10  
  Purchase #3 $57.65   5.331%   $60.7233   $60.72   $60.70   $60.70  
  Purchase #4 $103.43   8.524%   $112.2464   $112.25   $112.25   $112.20  
  Purchase #5 $25.37   9.108%   $27.6807   $27.68   $27.70   $27.70  
  Purchase #6 $191.36   3.554%   $198.1609   $198.16   $198.15   $198.20  
  Purchase #7 $127.39   12.261%   $143.0093   $143.01   $143.00   $143.00  
  7 purchase totals = $927.14       $1,005.1734   $1,005.18   $1,005.15   $1,005.20