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 $186.37   13.740%   $211.9772   $211.98   $212.00   $212.00  
  Purchase #2 $173.62   7.323%   $186.3342   $186.33   $186.35   $186.30  
  Purchase #3 $89.35   7.489%   $96.0414   $96.04   $96.05   $96.00  
  Purchase #4 $95.75   9.636%   $104.9765   $104.98   $105.00   $105.00  
  Purchase #5 $59.41   11.450%   $66.2124   $66.21   $66.20   $66.20  
  Purchase #6 $161.44   3.652%   $167.3358   $167.34   $167.35   $167.30  
  Purchase #7 $14.41   8.286%   $15.604   $15.60   $15.60   $15.60  
  7 purchase totals = $780.35       $848.4815   $848.48   $848.55   $848.40