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 $230.94   6.238%   $245.346   $245.35   $245.35   $245.30  
  Purchase #2 $248.67   11.751%   $277.8912   $277.89   $277.90   $277.90  
  Purchase #3 $119.28   4.116%   $124.1896   $124.19   $124.20   $124.20  
  Purchase #4 $94.25   12.467%   $106.0001   $106.00   $106.00   $106.00  
  Purchase #5 $240.32   9.554%   $263.2802   $263.28   $263.30   $263.30  
  Purchase #6 $19.25   6.809%   $20.5607   $20.56   $20.55   $20.60  
  Purchase #7 $219.84   4.647%   $230.056   $230.06   $230.05   $230.10  
  7 purchase totals = $1,172.55       $1,267.3238   $1,267.33   $1,267.35   $1,267.40