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 $156.44   8.212%   $169.2869   $169.29   $169.30   $169.30  
  Purchase #2 $110.65   8.620%   $120.188   $120.19   $120.20   $120.20  
  Purchase #3 $138.67   6.603%   $147.8264   $147.83   $147.85   $147.80  
  Purchase #4 $64.87   6.298%   $68.9555   $68.96   $68.95   $69.00  
  Purchase #5 $205.74   11.634%   $229.6758   $229.68   $229.70   $229.70  
  Purchase #6 $70.46   9.309%   $77.0191   $77.02   $77.00   $77.00  
  Purchase #7 $239.85   3.487%   $248.2136   $248.21   $248.20   $248.20  
  7 purchase totals = $986.68       $1,061.1653   $1,061.18   $1,061.20   $1,061.20