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 $222.39   13.180%   $251.701   $251.70   $251.70   $251.70  
  Purchase #2 $33.38   11.615%   $37.2571   $37.26   $37.25   $37.30  
  Purchase #3 $164.45   9.696%   $180.3951   $180.40   $180.40   $180.40  
  Purchase #4 $161.72   13.170%   $183.0185   $183.02   $183.00   $183.00  
  Purchase #5 $161.90   3.631%   $167.7786   $167.78   $167.80   $167.80  
  Purchase #6 $189.34   7.672%   $203.8662   $203.87   $203.85   $203.90  
  Purchase #7 $135.31   5.499%   $142.7507   $142.75   $142.75   $142.80  
  7 purchase totals = $1,068.49       $1,166.7672   $1,166.78   $1,166.75   $1,166.90