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 $201.40   11.557%   $224.6758   $224.68   $224.70   $224.70  
  Purchase #2 $23.68   4.234%   $24.6826   $24.68   $24.70   $24.70  
  Purchase #3 $119.28   12.526%   $134.221   $134.22   $134.20   $134.20  
  Purchase #4 $228.40   7.847%   $246.3225   $246.32   $246.30   $246.30  
  Purchase #5 $19.43   6.561%   $20.7048   $20.70   $20.70   $20.70  
  Purchase #6 $210.61   11.503%   $234.8365   $234.84   $234.85   $234.80  
  Purchase #7 $109.75   11.415%   $122.278   $122.28   $122.30   $122.30  
  7 purchase totals = $912.55       $1,007.7212   $1,007.72   $1,007.75   $1,007.70