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 $165.68   11.707%   $185.0762   $185.08   $185.10   $185.10  
  Purchase #2 $82.71   13.645%   $93.9958   $94.00   $94.00   $94.00  
  Purchase #3 $98.48   11.689%   $109.9913   $109.99   $110.00   $110.00  
  Purchase #4 $78.66   8.766%   $85.5553   $85.56   $85.55   $85.60  
  Purchase #5 $243.78   3.145%   $251.4469   $251.45   $251.45   $251.40  
  Purchase #6 $162.33   8.690%   $176.4365   $176.44   $176.45   $176.40  
  Purchase #7 $236.69   11.829%   $264.6881   $264.69   $264.70   $264.70  
  7 purchase totals = $1,068.33       $1,167.1901   $1,167.21   $1,167.25   $1,167.20