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 $37.93   11.365%   $42.2407   $42.24   $42.25   $42.20  
  Purchase #2 $183.26   10.483%   $202.4711   $202.47   $202.45   $202.50  
  Purchase #3 $243.38   9.734%   $267.0706   $267.07   $267.05   $267.10  
  Purchase #4 $64.88   6.358%   $69.0051   $69.01   $69.00   $69.00  
  Purchase #5 $246.70   5.623%   $260.5719   $260.57   $260.55   $260.60  
  Purchase #6 $144.41   4.409%   $150.777   $150.78   $150.80   $150.80  
  Purchase #7 $114.72   5.874%   $121.4587   $121.46   $121.45   $121.50  
  7 purchase totals = $1,035.28       $1,113.5951   $1,113.60   $1,113.55   $1,113.70