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 $246.82   3.289%   $254.9379   $254.94   $254.95   $254.90  
  Purchase #2 $14.71   11.718%   $16.4337   $16.43   $16.45   $16.40  
  Purchase #3 $131.62   4.673%   $137.7706   $137.77   $137.75   $137.80  
  Purchase #4 $162.33   11.820%   $181.5174   $181.52   $181.50   $181.50  
  Purchase #5 $198.28   13.856%   $225.7537   $225.75   $225.75   $225.80  
  Purchase #6 $178.64   7.767%   $192.515   $192.52   $192.50   $192.50  
  Purchase #7 $24.36   3.268%   $25.1561   $25.16   $25.15   $25.20  
  7 purchase totals = $956.76       $1,034.0844   $1,034.09   $1,034.05   $1,034.10