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 $173.46   5.668%   $183.2917   $183.29   $183.30   $183.30  
  Purchase #2 $221.52   11.103%   $246.1154   $246.12   $246.10   $246.10  
  Purchase #3 $82.41   10.580%   $91.129   $91.13   $91.15   $91.10  
  Purchase #4 $145.99   5.257%   $153.6647   $153.66   $153.65   $153.70  
  Purchase #5 $220.47   4.114%   $229.5401   $229.54   $229.55   $229.50  
  Purchase #6 $6.44   6.321%   $6.8471   $6.85   $6.85   $6.80  
  Purchase #7 $118.56   6.488%   $126.2522   $126.25   $126.25   $126.30  
  7 purchase totals = $968.85       $1,036.8402   $1,036.84   $1,036.85   $1,036.80