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 $64.51   10.156%   $71.0616   $71.06   $71.05   $71.10  
  Purchase #2 $204.69   13.338%   $231.9916   $231.99   $232.00   $232.00  
  Purchase #3 $128.77   12.588%   $144.9796   $144.98   $145.00   $145.00  
  Purchase #4 $98.30   8.718%   $106.8698   $106.87   $106.85   $106.90  
  Purchase #5 $246.50   13.637%   $280.1152   $280.12   $280.10   $280.10  
  Purchase #6 $27.79   6.262%   $29.5302   $29.53   $29.55   $29.50  
  Purchase #7 $154.80   10.190%   $170.5741   $170.57   $170.55   $170.60  
  7 purchase totals = $925.36       $1,035.1221   $1,035.12   $1,035.10   $1,035.20