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 $84.65   8.478%   $91.8266   $91.83   $91.85   $91.80  
  Purchase #2 $115.57   6.158%   $122.6868   $122.69   $122.70   $122.70  
  Purchase #3 $68.62   13.656%   $77.9907   $77.99   $78.00   $78.00  
  Purchase #4 $94.31   6.360%   $100.3081   $100.31   $100.30   $100.30  
  Purchase #5 $153.33   7.449%   $164.7516   $164.75   $164.75   $164.80  
  Purchase #6 $189.99   5.117%   $199.7118   $199.71   $199.70   $199.70  
  Purchase #7 $232.67   6.780%   $248.445   $248.45   $248.45   $248.40  
  7 purchase totals = $939.14       $1,005.7206   $1,005.73   $1,005.75   $1,005.70