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 $208.59   12.349%   $234.3488   $234.35   $234.35   $234.30  
  Purchase #2 $179.82   12.164%   $201.6933   $201.69   $201.70   $201.70  
  Purchase #3 $86.95   7.200%   $93.2104   $93.21   $93.20   $93.20  
  Purchase #4 $180.79   9.560%   $198.0735   $198.07   $198.05   $198.10  
  Purchase #5 $128.52   9.720%   $141.0121   $141.01   $141.00   $141.00  
  Purchase #6 $160.97   7.278%   $172.6854   $172.69   $172.70   $172.70  
  Purchase #7 $213.48   12.713%   $240.6197   $240.62   $240.60   $240.60  
  7 purchase totals = $1,159.12       $1,281.6432   $1,281.64   $1,281.60   $1,281.60