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 $245.36   6.217%   $260.614   $260.61   $260.60   $260.60  
  Purchase #2 $234.52   9.388%   $256.5367   $256.54   $256.55   $256.50  
  Purchase #3 $49.57   3.648%   $51.3783   $51.38   $51.40   $51.40  
  Purchase #4 $44.74   5.716%   $47.2973   $47.30   $47.30   $47.30  
  Purchase #5 $152.99   12.865%   $172.6722   $172.67   $172.65   $172.70  
  Purchase #6 $180.61   9.254%   $197.3236   $197.32   $197.30   $197.30  
  Purchase #7 $186.68   13.543%   $211.9621   $211.96   $211.95   $212.00  
  7 purchase totals = $1,094.47       $1,197.7842   $1,197.78   $1,197.75   $1,197.80