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 $118.66   9.220%   $129.6005   $129.60   $129.60   $129.60  
  Purchase #2 $156.64   5.148%   $164.7038   $164.70   $164.70   $164.70  
  Purchase #3 $213.84   10.242%   $235.7415   $235.74   $235.75   $235.70  
  Purchase #4 $109.80   13.618%   $124.7526   $124.75   $124.75   $124.80  
  Purchase #5 $182.72   10.430%   $201.7777   $201.78   $201.80   $201.80  
  Purchase #6 $33.69   8.823%   $36.6625   $36.66   $36.65   $36.70  
  Purchase #7 $123.73   13.851%   $140.8678   $140.87   $140.85   $140.90  
  7 purchase totals = $939.08       $1,034.1064   $1,034.10   $1,034.10   $1,034.20