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 $94.91   12.661%   $106.9266   $106.93   $106.95   $106.90  
  Purchase #2 $250.49   3.220%   $258.5558   $258.56   $258.55   $258.60  
  Purchase #3 $146.84   7.343%   $157.6225   $157.62   $157.60   $157.60  
  Purchase #4 $239.56   6.218%   $254.4558   $254.46   $254.45   $254.50  
  Purchase #5 $109.47   6.796%   $116.9096   $116.91   $116.90   $116.90  
  Purchase #6 $93.46   9.515%   $102.3527   $102.35   $102.35   $102.40  
  Purchase #7 $35.74   8.489%   $38.774   $38.77   $38.75   $38.80  
  7 purchase totals = $970.47       $1,035.5970   $1,035.60   $1,035.55   $1,035.70