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 $63.34   11.152%   $70.4037   $70.40   $70.40   $70.40  
  Purchase #2 $97.65   12.187%   $109.5506   $109.55   $109.55   $109.60  
  Purchase #3 $212.38   11.551%   $236.912   $236.91   $236.90   $236.90  
  Purchase #4 $81.44   4.132%   $84.8051   $84.81   $84.80   $84.80  
  Purchase #5 $195.48   12.701%   $220.3079   $220.31   $220.30   $220.30  
  Purchase #6 $34.41   8.614%   $37.3741   $37.37   $37.35   $37.40  
  Purchase #7 $246.96   4.711%   $258.5943   $258.59   $258.60   $258.60  
  7 purchase totals = $931.66       $1,017.9477   $1,017.94   $1,017.90   $1,018.00