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 $40.32   10.771%   $44.6629   $44.66   $44.65   $44.70  
  Purchase #2 $172.52   12.459%   $194.0143   $194.01   $194.00   $194.00  
  Purchase #3 $134.91   11.682%   $150.6702   $150.67   $150.65   $150.70  
  Purchase #4 $198.73   10.260%   $219.1197   $219.12   $219.10   $219.10  
  Purchase #5 $242.48   5.772%   $256.4759   $256.48   $256.50   $256.50  
  Purchase #6 $245.46   9.584%   $268.9849   $268.98   $269.00   $269.00  
  Purchase #7 $134.46   5.828%   $142.2963   $142.30   $142.30   $142.30  
  7 purchase totals = $1,168.88       $1,276.2242   $1,276.22   $1,276.20   $1,276.30