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 $54.29   6.526%   $57.833   $57.83   $57.85   $57.80  
  Purchase #2 $88.40   3.573%   $91.5585   $91.56   $91.55   $91.60  
  Purchase #3 $68.33   4.198%   $71.1985   $71.20   $71.20   $71.20  
  Purchase #4 $217.84   4.651%   $227.9717   $227.97   $227.95   $228.00  
  Purchase #5 $156.48   3.129%   $161.3763   $161.38   $161.40   $161.40  
  Purchase #6 $89.94   7.629%   $96.8015   $96.80   $96.80   $96.80  
  Purchase #7 $70.55   11.872%   $78.9257   $78.93   $78.95   $78.90  
  7 purchase totals = $745.83       $785.6652   $785.67   $785.70   $785.70