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 $228.98   12.527%   $257.6643   $257.66   $257.65   $257.70  
  Purchase #2 $201.38   12.503%   $226.5585   $226.56   $226.55   $226.60  
  Purchase #3 $130.93   6.255%   $139.1197   $139.12   $139.10   $139.10  
  Purchase #4 $57.46   5.595%   $60.6749   $60.67   $60.65   $60.70  
  Purchase #5 $54.77   9.802%   $60.1386   $60.14   $60.15   $60.10  
  Purchase #6 $233.37   3.589%   $241.7456   $241.75   $241.75   $241.70  
  Purchase #7 $82.35   11.180%   $91.5567   $91.56   $91.55   $91.60  
  7 purchase totals = $989.24       $1,077.4583   $1,077.46   $1,077.40   $1,077.50