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 $144.29   13.471%   $163.7273   $163.73   $163.75   $163.70  
  Purchase #2 $148.53   10.635%   $164.3262   $164.33   $164.35   $164.30  
  Purchase #3 $243.31   11.592%   $271.5145   $271.51   $271.50   $271.50  
  Purchase #4 $7.79   6.696%   $8.3116   $8.31   $8.30   $8.30  
  Purchase #5 $47.40   6.444%   $50.4545   $50.45   $50.45   $50.50  
  Purchase #6 $181.74   3.119%   $187.4085   $187.41   $187.40   $187.40  
  Purchase #7 $149.92   12.285%   $168.3377   $168.34   $168.35   $168.30  
  7 purchase totals = $922.98       $1,014.0803   $1,014.08   $1,014.10   $1,014.00