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 $235.58   13.587%   $267.5883   $267.59   $267.60   $267.60  
  Purchase #2 $96.72   11.836%   $108.1678   $108.17   $108.15   $108.20  
  Purchase #3 $13.49   11.349%   $15.021   $15.02   $15.00   $15.00  
  Purchase #4 $224.28   9.515%   $245.6202   $245.62   $245.60   $245.60  
  Purchase #5 $113.97   6.424%   $121.2914   $121.29   $121.30   $121.30  
  Purchase #6 $175.55   11.273%   $195.3398   $195.34   $195.35   $195.30  
  Purchase #7 $137.52   7.436%   $147.746   $147.75   $147.75   $147.70  
  7 purchase totals = $997.11       $1,100.7745   $1,100.78   $1,100.75   $1,100.70