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 $59.56   10.533%   $65.8335   $65.83   $65.85   $65.80  
  Purchase #2 $200.61   9.403%   $219.4734   $219.47   $219.45   $219.50  
  Purchase #3 $62.57   11.394%   $69.6992   $69.70   $69.70   $69.70  
  Purchase #4 $148.66   10.852%   $164.7926   $164.79   $164.80   $164.80  
  Purchase #5 $14.60   4.664%   $15.2809   $15.28   $15.30   $15.30  
  Purchase #6 $212.79   11.417%   $237.0842   $237.08   $237.10   $237.10  
  Purchase #7 $246.93   6.488%   $262.9508   $262.95   $262.95   $263.00  
  7 purchase totals = $945.72       $1,035.1146   $1,035.10   $1,035.15   $1,035.20