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 $66.82   11.266%   $74.3479   $74.35   $74.35   $74.30  
  Purchase #2 $212.99   7.179%   $228.2806   $228.28   $228.30   $228.30  
  Purchase #3 $201.98   4.503%   $211.0752   $211.08   $211.10   $211.10  
  Purchase #4 $246.38   7.194%   $264.1046   $264.10   $264.10   $264.10  
  Purchase #5 $87.32   3.768%   $90.6102   $90.61   $90.60   $90.60  
  Purchase #6 $170.61   6.625%   $181.9129   $181.91   $181.90   $181.90  
  Purchase #7 $199.98   8.413%   $216.8043   $216.80   $216.80   $216.80  
  7 purchase totals = $1,186.08       $1,267.1357   $1,267.13   $1,267.15   $1,267.10