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 $246.94   13.652%   $280.6522   $280.65   $280.65   $280.70  
  Purchase #2 $186.52   9.121%   $203.5325   $203.53   $203.55   $203.50  
  Purchase #3 $249.62   3.742%   $258.9608   $258.96   $258.95   $259.00  
  Purchase #4 $104.50   3.657%   $108.3216   $108.32   $108.30   $108.30  
  Purchase #5 $138.50   5.276%   $145.8073   $145.81   $145.80   $145.80  
  Purchase #6 $205.67   6.212%   $218.4462   $218.45   $218.45   $218.40  
  Purchase #7 $229.49   6.298%   $243.9433   $243.94   $243.95   $243.90  
  7 purchase totals = $1,361.24       $1,459.6639   $1,459.66   $1,459.65   $1,459.60