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 $41.54   3.796%   $43.1169   $43.12   $43.10   $43.10  
  Purchase #2 $166.56   6.351%   $177.1382   $177.14   $177.15   $177.10  
  Purchase #3 $84.92   6.128%   $90.1239   $90.12   $90.10   $90.10  
  Purchase #4 $235.95   11.373%   $262.7846   $262.78   $262.80   $262.80  
  Purchase #5 $220.65   10.672%   $244.1978   $244.20   $244.20   $244.20  
  Purchase #6 $124.58   4.674%   $130.4029   $130.40   $130.40   $130.40  
  Purchase #7 $115.55   11.365%   $128.6823   $128.68   $128.70   $128.70  
  7 purchase totals = $989.75       $1,076.4466   $1,076.44   $1,076.45   $1,076.40