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 $127.76   5.673%   $135.0078   $135.01   $135.00   $135.00  
  Purchase #2 $142.52   9.175%   $155.5962   $155.60   $155.60   $155.60  
  Purchase #3 $193.58   8.831%   $210.675   $210.68   $210.70   $210.70  
  Purchase #4 $59.65   12.368%   $67.0275   $67.03   $67.05   $67.00  
  Purchase #5 $216.50   4.412%   $226.052   $226.05   $226.05   $226.10  
  Purchase #6 $172.79   6.469%   $183.9678   $183.97   $183.95   $184.00  
  Purchase #7 $119.32   11.468%   $133.0036   $133.00   $133.00   $133.00  
  7 purchase totals = $1,032.12       $1,111.3299   $1,111.34   $1,111.35   $1,111.40