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 $35.78   4.320%   $37.3257   $37.33   $37.35   $37.30  
  Purchase #2 $210.70   9.564%   $230.8513   $230.85   $230.85   $230.90  
  Purchase #3 $97.57   12.773%   $110.0326   $110.03   $110.05   $110.00  
  Purchase #4 $44.58   9.747%   $48.9252   $48.93   $48.95   $48.90  
  Purchase #5 $211.59   13.796%   $240.781   $240.78   $240.80   $240.80  
  Purchase #6 $198.64   8.594%   $215.7111   $215.71   $215.70   $215.70  
  Purchase #7 $127.38   4.724%   $133.3974   $133.40   $133.40   $133.40  
  7 purchase totals = $926.24       $1,017.0243   $1,017.03   $1,017.10   $1,017.00