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 $86.44   7.836%   $93.2134   $93.21   $93.20   $93.20  
  Purchase #2 $201.27   4.158%   $209.6388   $209.64   $209.65   $209.60  
  Purchase #3 $207.67   8.708%   $225.7539   $225.75   $225.75   $225.80  
  Purchase #4 $201.52   7.566%   $216.767   $216.77   $216.75   $216.80  
  Purchase #5 $190.51   4.460%   $199.0067   $199.01   $199.00   $199.00  
  Purchase #6 $94.72   3.467%   $98.0039   $98.00   $98.00   $98.00  
  Purchase #7 $213.38   4.853%   $223.7353   $223.74   $223.75   $223.70  
  7 purchase totals = $1,195.51       $1,266.1190   $1,266.12   $1,266.10   $1,266.10