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 $167.63   13.456%   $190.1863   $190.19   $190.20   $190.20  
  Purchase #2 $113.37   3.842%   $117.7257   $117.73   $117.75   $117.70  
  Purchase #3 $175.25   3.220%   $180.8931   $180.89   $180.90   $180.90  
  Purchase #4 $222.52   10.811%   $246.5766   $246.58   $246.60   $246.60  
  Purchase #5 $119.90   3.415%   $123.9946   $123.99   $124.00   $124.00  
  Purchase #6 $124.84   9.835%   $137.118   $137.12   $137.10   $137.10  
  Purchase #7 $63.48   10.402%   $70.0832   $70.08   $70.10   $70.10  
  7 purchase totals = $986.99       $1,066.5775   $1,066.58   $1,066.65   $1,066.60