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 $36.72   10.288%   $40.4978   $40.50   $40.50   $40.50  
  Purchase #2 $93.87   9.816%   $103.0843   $103.08   $103.10   $103.10  
  Purchase #3 $212.25   3.687%   $220.0757   $220.08   $220.10   $220.10  
  Purchase #4 $216.31   12.191%   $242.6804   $242.68   $242.70   $242.70  
  Purchase #5 $231.84   13.803%   $263.8409   $263.84   $263.85   $263.80  
  Purchase #6 $223.60   10.560%   $247.2122   $247.21   $247.20   $247.20  
  Purchase #7 $25.97   8.785%   $28.2515   $28.25   $28.25   $28.30  
  7 purchase totals = $1,040.56       $1,145.6428   $1,145.64   $1,145.70   $1,145.70