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 $218.44   11.691%   $243.9778   $243.98   $244.00   $244.00  
  Purchase #2 $236.25   4.137%   $246.0237   $246.02   $246.00   $246.00  
  Purchase #3 $32.30   6.837%   $34.5084   $34.51   $34.50   $34.50  
  Purchase #4 $80.47   5.313%   $84.7454   $84.75   $84.75   $84.70  
  Purchase #5 $6.45   9.803%   $7.0823   $7.08   $7.10   $7.10  
  Purchase #6 $19.52   12.585%   $21.9766   $21.98   $22.00   $22.00  
  Purchase #7 $193.69   6.498%   $206.276   $206.28   $206.30   $206.30  
  7 purchase totals = $787.12       $844.5902   $844.60   $844.65   $844.60