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 $232.75   8.673%   $252.9364   $252.94   $252.95   $252.90  
  Purchase #2 $108.33   9.466%   $118.5845   $118.58   $118.60   $118.60  
  Purchase #3 $69.78   4.251%   $72.7463   $72.75   $72.75   $72.70  
  Purchase #4 $184.72   9.784%   $202.793   $202.79   $202.80   $202.80  
  Purchase #5 $64.56   5.835%   $68.3271   $68.33   $68.35   $68.30  
  Purchase #6 $148.85   5.804%   $157.4893   $157.49   $157.50   $157.50  
  Purchase #7 $204.51   12.653%   $230.3867   $230.39   $230.40   $230.40  
  7 purchase totals = $1,013.50       $1,103.2633   $1,103.27   $1,103.35   $1,103.20