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 $61.50   11.236%   $68.4101   $68.41   $68.40   $68.40  
  Purchase #2 $118.31   6.699%   $126.2356   $126.24   $126.25   $126.20  
  Purchase #3 $159.48   13.764%   $181.4308   $181.43   $181.45   $181.40  
  Purchase #4 $89.80   3.331%   $92.7912   $92.79   $92.80   $92.80  
  Purchase #5 $142.99   12.502%   $160.8666   $160.87   $160.85   $160.90  
  Purchase #6 $243.60   9.804%   $267.4825   $267.48   $267.50   $267.50  
  Purchase #7 $114.61   6.658%   $122.2407   $122.24   $122.25   $122.20  
  7 purchase totals = $930.29       $1,019.4575   $1,019.46   $1,019.50   $1,019.40