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 $55.74   5.780%   $58.9618   $58.96   $58.95   $59.00  
  Purchase #2 $22.32   6.307%   $23.7277   $23.73   $23.75   $23.70  
  Purchase #3 $237.35   6.205%   $252.0776   $252.08   $252.10   $252.10  
  Purchase #4 $31.96   9.198%   $34.8997   $34.90   $34.90   $34.90  
  Purchase #5 $75.56   8.325%   $81.8504   $81.85   $81.85   $81.90  
  Purchase #6 $219.42   6.381%   $233.4212   $233.42   $233.40   $233.40  
  Purchase #7 $243.84   10.321%   $269.0067   $269.01   $269.00   $269.00  
  7 purchase totals = $886.19       $953.9451   $953.95   $953.95   $954.00