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 $211.99   9.760%   $232.6802   $232.68   $232.70   $232.70  
  Purchase #2 $145.28   11.582%   $162.1063   $162.11   $162.10   $162.10  
  Purchase #3 $119.37   3.437%   $123.4727   $123.47   $123.45   $123.50  
  Purchase #4 $68.94   4.250%   $71.87   $71.87   $71.85   $71.90  
  Purchase #5 $223.44   3.837%   $232.0134   $232.01   $232.00   $232.00  
  Purchase #6 $242.63   10.298%   $267.616   $267.62   $267.60   $267.60  
  Purchase #7 $79.39   12.569%   $89.3685   $89.37   $89.35   $89.40  
  7 purchase totals = $1,091.04       $1,179.1271   $1,179.13   $1,179.05   $1,179.20