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 $169.85   11.717%   $189.7513   $189.75   $189.75   $189.80  
  Purchase #2 $5.26   10.811%   $5.8287   $5.83   $5.85   $5.80  
  Purchase #3 $12.52   12.861%   $14.1302   $14.13   $14.15   $14.10  
  Purchase #4 $60.34   5.453%   $63.6303   $63.63   $63.65   $63.60  
  Purchase #5 $226.51   12.273%   $254.3096   $254.31   $254.30   $254.30  
  Purchase #6 $182.93   10.761%   $202.6151   $202.62   $202.60   $202.60  
  Purchase #7 $238.52   13.655%   $271.0899   $271.09   $271.10   $271.10  
  7 purchase totals = $895.93       $1,001.3551   $1,001.36   $1,001.40   $1,001.30