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 $176.80   11.788%   $197.6412   $197.64   $197.65   $197.60  
  Purchase #2 $130.46   8.794%   $141.9327   $141.93   $141.95   $141.90  
  Purchase #3 $36.56   8.264%   $39.5813   $39.58   $39.60   $39.60  
  Purchase #4 $184.58   7.262%   $197.9842   $197.98   $198.00   $198.00  
  Purchase #5 $172.72   10.869%   $191.4929   $191.49   $191.50   $191.50  
  Purchase #6 $203.79   11.310%   $226.8386   $226.84   $226.85   $226.80  
  Purchase #7 $73.32   6.702%   $78.2339   $78.23   $78.25   $78.20  
  7 purchase totals = $978.23       $1,073.7048   $1,073.69   $1,073.80   $1,073.60