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 $219.88   5.568%   $232.1229   $232.12   $232.10   $232.10  
  Purchase #2 $66.92   13.205%   $75.7568   $75.76   $75.75   $75.80  
  Purchase #3 $186.59   11.144%   $207.3836   $207.38   $207.40   $207.40  
  Purchase #4 $201.72   4.823%   $211.449   $211.45   $211.45   $211.40  
  Purchase #5 $162.45   10.214%   $179.0426   $179.04   $179.05   $179.00  
  Purchase #6 $198.38   11.541%   $221.275   $221.28   $221.30   $221.30  
  Purchase #7 $140.59   10.851%   $155.8454   $155.85   $155.85   $155.80  
  7 purchase totals = $1,176.53       $1,282.8753   $1,282.88   $1,282.90   $1,282.80