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 $167.84   8.470%   $182.056   $182.06   $182.05   $182.10  
  Purchase #2 $20.34   7.120%   $21.7882   $21.79   $21.80   $21.80  
  Purchase #3 $156.81   8.335%   $169.8801   $169.88   $169.90   $169.90  
  Purchase #4 $243.40   8.397%   $263.8383   $263.84   $263.85   $263.80  
  Purchase #5 $121.25   12.638%   $136.5736   $136.57   $136.55   $136.60  
  Purchase #6 $187.30   13.706%   $212.9713   $212.97   $212.95   $213.00  
  Purchase #7 $31.64   5.574%   $33.4036   $33.40   $33.40   $33.40  
  7 purchase totals = $928.58       $1,020.5111   $1,020.51   $1,020.50   $1,020.60